1. Technical Field
The present disclosure relates to flat panel loudspeakers, and particularly, to a flat panel piezoelectric loudspeaker (hereinafter, “FPPL”).
2. Description of Related Art
The operating principle of FPPLs is based on a converse piezoelectric effect of some piezoelectric material. Namely, when an alternating electric field is applied to the piezoelectric material, the piezoelectric material can be correspondingly and mechanically distorted, thereby triggering sound producing vibration of ambient air.
Currently, the basic structure of the FPPL includes a piezoelectric element, a first electrode, and a second electrode. The first electrode and the second electrode are electrically connected to the piezoelectric element, and spaced apart. Conventionally, the first electrode and the second electrode are fabricatable via printing metal film on the piezoelectric element, to electrically connect with the piezoelectric element seamlessly. During operation of the FPPL, the piezoelectric element is mechanically and repeatedly bent or distorted. However, the first electrode and the second electrode consist of metal, and have a poor anti-fatigue performance due to a fatigue fracture derived from the distortion of the piezoelectric element.
For achieving a transparent FPPL, the first electrode and the second electrode can consist of indium tin oxide (ITO) layer which has poor flexibility and anti-fatigue performance and thus is easily breakable because of the fatigue fracture. Moreover, because the ITO layer can only be deposited on a surface of the piezoelectric element under high temperatures, the piezoelectric performance of the piezoelectric element may be adversely affected by the ITO layer deposit process.
Carbon nanotube films can be used as electrodes of a conventional transparent FPPL. The method of forming the carbon nanotube film on the piezoelectric element includes coating the liquid solution comprising carbon nanotubes on two surfaces of the piezoelectric element, and vaporizing solvent in the liquid solution under a temperature in a range from 50 degrees to 70 degrees. In this method, the carbon nanotube film is formed on the piezoelectric element under a low temperature, and the piezoelectric performance would not decline under this low temperature. However, the carbon nanotubes in the carbon nanotube film are disorderly arranged, thus, the conductive property of the carbon nanotubes cannot be applied adequately, thereby slowing the response speed of the flat panel loudspeaker.
What is needed, therefore, is an improved FPPL having a fast response.